Coated medical devices, particularly endoluminally deployable medical devices, are known for a variety of medical applications. In the case of an implantable medical device, that is a device intended to be left in the patient permanently or over long periods of time, the device may coated with one or more layers of drugs intended for long term drug administration to diseased tissue. Treatment of cancers is an example. In other examples, the coating is provided in order to treat adverse body reactions caused by the medical treatment or by long term presence of a foreign object in the body, such as initial reactive hyperplasia, inflammation, thrombosis, restenosis and so on. In these cases the medical device is deployed only temporarily in a patient.
It is important that a bioactive coating on a medical device is consistent over the surface or surfaces of the device, is reliably formed from one device to another, is sufficiently well held on the device during deployment, and can be administered into the patient at the desired rate once the device is deployed. For instance, a coating on an implantable device such as a stent, filter, vascular plug or the like may need to be released over an extended period of time such as weeks, months or years, whereas a coating on a medical balloon, such as an angioplasty balloon or a device delivery balloon, may need to be released over a period of seconds or minutes.
Applying a bioactive agent to an untreated surface of a medical device often fails to form a uniform or reliable coating, leading to variable bioactive results. This is particularly the case with lipophilic materials including, for instance, paclitaxel, which has been proven to be a very effective anti-restenosis drug.
Attempts have been made in the art to treat one or more surfaces of medical devices to improve their biocompatibility and also to seek to improve the adherence of one or more coatings onto the medical device. These known treatments, however, have failed to provide consistent, reliable and repeatable surface characteristics for many bioactive agents. Failure to provide an adequate coating can result in failure to meet the strict drug release required by the FDA USP pharmacopeia drug device requirements and that of other regulatory bodies.
Other attempts in the art have involved providing for containment of the bioactive agent, for instance in a containment device such as a polymer matrix, by applying an outer layer or coat over the layer of bioactive material, by encapsulating the bioactive agent in capsules or other carriers, and so on. Such containment mechanisms, which restrain the bioactive material on the device and control the release of the material into the patient, can often cause other clinical issues, including reduction in the amount of bioactive material which can be carried on the medical device and inadequate release rate of the bioactive material. Furthermore, the containment device can act as a target for long term restenosis and other foreign body reactions. Despite such drawbacks, containment devices are still often proposed in order to seek to overcome the difficulty of adequately holding the bioactive material to the medical device and of ensuring adequate dosage of bioactive material in order to try to meet regulatory criteria.
Some examples of known surface treatments are disclosed in U.S. Pat. Nos. 7,597,924, 7,396,582, 6,632,470, 8,123,799, 9,005,960 and US-2009/171453, the contents of which application are hereby incorporated by reference.